Electronic Stability Control (ESC) is the generic term for systems designed to improve a motor vehicle's handling, particularly at the limits where the driver might lose control of the motor vehicle. See, for example, the Society of Automotive Engineers (SAE) document on “Automotive Stability Enhancement Systems”, publication J2564 (Dec. 2000, Jun. 2004). ESC compares the driver's intended direction in steering and braking inputs to the motor vehicle's response, via lateral acceleration, rotation (yaw) and individual wheel speeds, and then brakes individual front or rear wheels and/or reduces excess engine power as needed to help correct understeer (plowing) or oversteer (fishtailing). ESC also integrates all-speed traction control which senses drive-wheel slip under acceleration and individually brakes the slipping wheel or wheels, and/or reduces excess engine power until control is regained. ESC cannot override a car's physical limits. Of course, if a driver pushes the possibilities of the car's chassis and ESC too far, ESC cannot prevent a crash. It is a tool to help the driver maintain control. ESC combines anti-lock brakes, traction control and yaw control (yaw is spin around the vertical axis).
ESC systems use several sensors in order to determine the state the driver wants the motor vehicle to be in (driver demand). Other sensors indicate the actual state of the motor vehicle (motor vehicle response). The ESC control algorithm compares both states and decides, when necessary, to adjust the dynamic state of the motor vehicle. The sensors used for ESC have to send data at all times in order to detect possible defects as soon as possible. They have to be resistant to possible forms of interference (rain, potholes in the road, etc.). The most important sensors are: 1) steering wheel sensor, used to determine the angle the driver wants to take, often based on anisotropic magnetoresistive (AMR) elements; 2) lateral acceleration sensor, used to measure the lateral acceleration of the motor vehicle; 3) yaw sensor, used to measure the yaw angle (rotation) of the motor vehicle, can be compared by the ESC with the data from the steering wheel sensor in order to take a regulating action; and 4) wheel speed sensors used to measure the wheel speeds.
ESC uses, for example, a hydraulic modulator to assure that each wheel receives the correct brake force. A similar modulator is used with anti-lock brake systems (ABS). ABS needs to reduce pressure during braking only. ESC additionally needs to increase brake pressure in certain situations.
The heart of the ESC system is the electronic control unit (ECU) or electronic control module (ECM), i.e., motor vehicle controller or microprocessor. Diverse control techniques are embedded in the ECU and often, the same ECU is used for diverse systems at the same time (ABS, traction control, climate control, etc.). The desired motor vehicle state is determined based on the steering wheel angle, its gradient and the wheel speed. Simultaneously, the yaw sensor measures the actual state. The controller computes the needed brake or acceleration force for each wheel and directs the actuation of, for example, the valves of a hydraulic brake modulator.
Motor vehicles utilizing electronic stability control systems require some means of determination of the driver's intended motor vehicle behavior (i.e., intended motor vehicle path or track). In General Motors Corporation's (GM's) StabiliTrak system, these means are accomplished by the driver command interpreter, as described in U.S. Pat. No. 5,941,919, issued Aug. 24, 1999 to the assignee hereof, the entire disclosure of which patent is hereby herein incorporated by reference.
Referring now to FIG. 1, the exemplar control structure described in U.S. Pat. No. 5,941,919 is shown. The controller 10 includes command interpreter 12 receiving the various system inputs 14 from various vehicle sensors. The command interpreter 12 develops desired yaw rate commands responsive to the various system inputs and a data structure 16 stored in non-volatile memory of controller 10. The data structure 16 has a data subset 18 corresponding to vehicle operation in linear mode and a data subset 20 corresponding to vehicle operation in non-linear mode.
When the vehicle operation is in the linear mode, the command interpreter 12, using data structure subset 18, provides commands to a control block 22 designed to maintain the linear response of the vehicle. For example, when the control according to this patent is used to control wheel brakes to affect vehicle yaw control, the commands provided by block 12 do not modify the wheel brake operation while the vehicle is in the linear mode. When the control according to this patent is used to control a vehicle variable force suspension system, the suspension control is provided to maintain the current driving conditions, and not to induce a change in understeer or oversteer.
When the vehicle operation is in the non-linear region, the command interpreter 12, using data structure subset 20, provides commands to the control block 22 commanding a yaw rate linearly responsive to the vehicle steering wheel input. Block 22 uses the command generated at block 12 to control one or more vehicle chassis systems, such as controllable suspension actuators, represented by block 24 and/or brakes, represented by block 26 to bring the actual vehicle yaw into a linear relationship with vehicle steering wheel angle. This control thus maintains the yaw response of the vehicle linear with respect to the steering wheel input even when the vehicle is operating in its nonlinear performance region.
Collision preparation systems are known in the art, as for example exemplified by U.S. Pat. No. 7,280,902 which discloses a motor vehicle deceleration control apparatus; U.S. Pat. No. 7,035,735 which discloses a method and device for automatically triggering a deceleration of a motor vehicle; and U.S. Patent Application Publication 2004/0254729 which discloses a pre-collision assessment of potential collision severity for motor vehicles.
Of particular interest with regard to the present invention, are U.S. Pat. No. 5,952,939, issued Sep. 14, 1999; U.S. Pat. No. 6,226,593, issued May 1, 2001; U.S. Pat. No. 6,084,508, issued Jul. 4, 2000; U.S. Pat. No. 6,517,172, issued Feb. 11, 2003; and U.S. Pat. No. 7,213,687, issued May 8, 2007; wherein the disclosures of all of the aforesaid patents (i.e., U.S. Pat. Nos. 5,952,939; 6,226,593; 6,084,508; 6,517,172; and 7,213,687) are hereby herein incorporated by reference.
U.S. Pat. No. 5,952,939 discloses a collision prevention device incorporating a vehicle braking force based on the comparison of the depression angle of the brake pedal and a calculated minimum required braking force to avoid a collision wherein the larger of these two forces is applied for braking.
U.S. Pat. No. 6,226,593 discloses a method for braking a motor vehicle at low speeds in order to avoid a collision with an obstacle in its immediate vicinity. The distance and the relative speed between the vehicle and the obstacle are determined by sensor and are based on the calculation of a necessary braking pressure or a deceleration. The brake pressure is generated at least partially independently of the driver.
U.S. Pat. No. 6,084,508 discloses a collision preparation system which provides autonomous braking in certain situations. The method and arrangement for emergency braking of a vehicle includes a detection system on the vehicle which detects obstacles located in or near the direction of motion of the vehicle and generates corresponding data, sensors on the vehicle which generate data representing characteristic parameters of the condition of the vehicle, and an evaluating unit which determines, from the data on the obstacles and the parameters of the condition of the vehicle, target values for controlling the motion of the vehicle and, only upon determining that an impending collision of the vehicle with an obstacle is no longer avoidable by any action on the vehicle by steering or braking, triggers an autonomous emergency braking for rapid deceleration of the vehicle.
U.S. Pat. No. 6,517,172 discloses a collision preparation system incorporating a brake assist system which provides autonomous braking in certain situations. When a forward detection apparatus detects an imminent collision, the braking system automatically applies braking force to the vehicle while the vehicle engine speed is reduced. The amount of brake force applied is a continuous function of relative speed, relative distance, collision probability, and target classification.
U.S. Pat. No. 7,213,687 discloses a collision preparation system which also incorporates a brake assist system which provides autonomous braking in certain situations. A vehicle emergency brake system has a second brake for braking a vehicle by increasing the frictional resistance with the road surface, a millimeter wave radar for detecting any obstacle in an advancing direction, pedal speed sensor for detecting the step-in speed of a brake pedal for actuating a first brake, and a controller for actuating the second brake.
The above-cited U.S. Patents provide for an automatic braking The automatic braking is either automatically initiated braking or braking which is initiated by the driver, but is performed automatically. Both possibilities share the feature, however, that a strong deceleration to avoid a collision or to reduce the collision speed may occur during braking, the deceleration of which corresponds to approximately the maximum possible vehicle deceleration.
Motor vehicle collision preparation systems (CPS) incorporating brake assist systems providing a calculated amount of braking (i.e. deceleration) required to avoid a collision with an obstacle when the vehicle driver thereafter applies the brakes are herein referred to as “integrated brake assist” (IBA) systems.
After actuation of a CPS incorporating an integrated brake assist system (IBA), the IBA constantly calculates the amount of braking (i.e., deceleration) required to avoid a collision with an obstacle. If the vehicle driver thereafter applies the brakes, the calculated amount of braking (i.e., deceleration) required to avoid a collision with an obstacle is automatically applied but never less than the driver requested braking. That is, if the driver requests more braking (i.e., more deceleration) than is to be applied, the driver requested braking is applied. However, the IBA may provide more deceleration of the vehicle than necessary in some circumstances. For example, for an accelerating obstacle or an obstacle which is soon to be out of the vehicle's path, less deceleration may be desired than is to be applied.
Accordingly, what is needed in the art is to provide vehicle multi-stage integrated brake assist, enabled after actuation of a CPS incorporating an IBA system, which can provide a brake assist level of a plurality of levels of brake assist (i.e., deceleration) less than or greater than the amount of braking (i.e., deceleration) required to avoid a collision with an obstacle but allows the driver to increase or remove the provided brake assist.